I have a 90 v. DC generator. I want to monitor the current using a data logger. I thought I would determine the resistance of a wire in circuit and monitor the voltage across it. The resolution of my ohmmeter is only 0.1 ohm.
How to do?
Take a very long length of the wire - say enough to give about 10 ohms resistance. Measure the length and the resistance. You can then work out what the resistance of a much shorter length of the wire will be, to a reasonable accuracy.
Alternatively, measure the diameter of the conductor, work out the cross-sectional area and calculate the resistance per unit length.
Or, just look the wire up in tables.
Your basic idea is sound but you would have to compensate for temperature changes in the wire.
Better off to go buy a commercial metering shunt. This is a 'precision resistance', but it has the advantage of being made from special materials whose resistance doesn't change much with temperature and designed with heat disipation fins so its temperature changes little.
Typical shunts are rated in 50 mV or 100 mV at rated current (e.g. 50 mV at
200A).Good luck
daestrom
What current do you expect to see at full load? Very small currents require a larger resistance meter shunt.
Place a DC ammeter in series with the motor and meter shunt. Add a trim pot to the shunt for calibration.
Calibrate the logger with the meter and don't worry to much about what the exact resistance of the shunt is.
PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.